This invention relates to microwave filters and, in particular, to waveguide filters employing dielectric resonators.
Practical mounting elements for dielectric resonators in conventional bandstop filters are available. See, for example, U.S. Pat. No. 4,124,830 issued to C. Ren on Nov. 7, 1978. The physical size, namely the length of this type of filters, as well as the other types of waveguide filters is related to the wavelength of the propagating electromagnetic field therein. Particularly in the case of multiple tone or bandstop filters, the longitudinal dimensions of conventionally designed filters increases when multiple tuned elements are used. Due to practical considerations, the tuned elements must be spaced at appropriate intervals to achieve rejection at desired attenuation levels. In particular, multiple pole filtering characteristics typically requires the cooperation of a plurality of resonators working at peak efficiency to achieve a desired response as depicted by the shape of the attenuation curve in the bandstop region.